Maximize length of subarray of equal elements by performing at most K increment operations

Last Updated : 20 May, 2021

Given an array A[] consisting of N integers and an integer K, the task is to maximize the length of the subarray having equal elements after performing at most K increments by 1 on array elements.

Note: Same array element can be incremented more than once.

Examples:

Input: A[] = {2, 4, 8, 5, 9, 6}, K = 6
Output: 3
Explanation:
Subarray [8, 5, 9] can be modified to [9, 9, 9].
Total number of increments required is 5 which is less than K(= 6).

Input: A[] = {2, 2, 4}, K = 10
Output: 3

Naive Approach: The simplest approach to solve the problem is to generate all possible subarrays and for each subarray, check if all its elements can be made equal in at most K increments. Print the maximum length of such subarrays obtained.

Time Complexity: O(N³)
Auxiliary Space: O(1)

Approach: The above approach can be optimized using the Sliding Window technique. Follow the steps below to solve the problem:

Keep a track of the maximum element of the window.
The total operations required for a particular window is obtained by the following equation:

Count of operations = (Length of the window calculated so far + 1) * (Maximum element from the window) – Sum of the window

Now, check if the above-calculated value exceeds K or not. If so, then slide the starting pointer of the window towards the right, otherwise increment the length of the window calculated so far.
Repeat the above steps to obtain the longest window satisfying the required condition.

Below is the implementation of the above approach:

C++14

// C++14 program for above approach
#include <bits/stdc++.h>
using namespace std;
#define newl "\n"
 
// Function to find the maximum length
// of subarray of equal elements after
// performing at most K increments
int maxSubarray(int a[], int k, int n)
{
 
    // Stores the size
    // of required subarray
    int answer = 0;
 
    // Starting point of a window
    int start = 0;
 
    // Stores the sum of window
    long int s = 0;
 
    deque<int> dq;
 
    // Iterate over array
    for(int i = 0; i < n; i++) 
    {
         
        // Current element
        int x = a[i];
 
        // Remove index of minimum elements
        // from deque which are less than
        // the current element
        while (!dq.empty() &&
               a[dq.front()] <= x)
            dq.pop_front();
 
        // Insert current index in deque
        dq.push_back(i);
 
        // Update current window sum
        s += x;
 
        // Calculate required operation to
        // make current window elements equal
        long int cost = (long int)a[dq.front()] *
                        (answer + 1) - s;
 
        // If cost is less than k
        if (cost <= (long int)k)
            answer++;
 
        // Shift window start pointer towards
        // right and update current window sum
        else
        {
            if (dq.front() == start)
                dq.pop_front();
                 
            s -= a[start++];
        }
    }
     
    // Return answer
    return answer;
}
 
// Driver Code
int main()
{
    int a[] = { 2, 2, 4 };
    int k = 10;
     
    // Length of array
    int n = sizeof(a) / sizeof(a[0]);
     
    cout << (maxSubarray(a, k, n));
     
    return 0;
}
 
// This code is contributed by jojo9911

Java

// Java Program for above approach
import java.util.*;
 
class GFG {
 
    // Function to find the maximum length
    // of subarray of equal elements after
    // performing at most K increments
    static int maxSubarray(int[] a, int k)
    {
        // Length of array
        int n = a.length;
 
        // Stores the size
        // of required subarray
        int answer = 0;
 
        // Starting point of a window
        int start = 0;
 
        // Stores the sum of window
        long s = 0;
 
        Deque<Integer> dq = new LinkedList<>();
 
        // Iterate over array
        for (int i = 0; i < n; i++) {
 
            // Current element
            int x = a[i];
 
            // Remove index of minimum elements
            // from deque which are less than
            // the current element
            while (!dq.isEmpty() && a[dq.peek()] <= x)
                dq.poll();
 
            // Insert current index in deque
            dq.add(i);
 
            // Update current window sum
            s += x;
 
            // Calculate required operation to
            // make current window elements equal
            long cost
                = (long)a[dq.peekFirst()] * (answer + 1)
                  - s;
 
            // If cost is less than k
            if (cost <= (long)k)
                answer++;
 
            // Shift window start pointer towards
            // right and update current window sum
            else {
                if (dq.peekFirst() == start)
                    dq.pollFirst();
                s -= a[start++];
            }
        }
 
        // Return answer
        return answer;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
 
        int[] a = { 2, 2, 4 };
        int k = 10;
 
        // Function call
        System.out.println(maxSubarray(a, k));
    }
}

Python3

# Python3 program for above approach
from collections import deque
 
# Function to find the maximum length
# of subarray of equal elements after
# performing at most K increments
def maxSubarray(a, k):
     
    # Length of array
    n = len(a)
 
    # Stores the size
    # of required subarray
    answer = 0
 
    # Starting po of a window
    start = 0
 
    # Stores the sum of window
    s = 0
 
    dq = deque()
 
    # Iterate over array
    for i in range(n):
 
        # Current element
        x = a[i]
 
        # Remove index of minimum elements
        # from deque which are less than
        # the current element
        while (len(dq) > 0 and a[dq[-1]] <= x):
            dq.popleft()
 
        # Insert current index in deque
        dq.append(i)
 
        # Update current window sum
        s += x
 
        # Calculate required operation to
        # make current window elements equal
        cost = a[dq[0]] * (answer + 1) - s
 
        # If cost is less than k
        if (cost <= k):
            answer += 1
 
        # Shift window start pointer towards
        # right and update current window sum
        else:
            if (dq[0] == start):
                dq.popleft()
                 
            s -= a[start]
            start += 1
 
    # Return answer
    return answer
 
# Driver Code
if __name__ == '__main__':
     
    a = [ 2, 2, 4 ]
    k = 10
 
    # Function call
    print(maxSubarray(a, k))
 
# This code is contributed by mohit kumar 29

C#

// C# Program for
// the above approach
using System;
using System.Collections.Generic;
class GFG{
 
// Function to find the maximum length
// of subarray of equal elements after
// performing at most K increments
static int maxSubarray(int[] a, int k)
{
  // Length of array
  int n = a.Length;
 
  // Stores the size
  // of required subarray
  int answer = 0;
 
  // Starting point of a window
  int start = 0;
 
  // Stores the sum of window
  long s = 0;
 
  Queue<int> dq = new Queue<int>();
 
  // Iterate over array
  for (int i = 0; i < n; i++)
  {
    // Current element
    int x = a[i];
 
    // Remove index of minimum 
    // elements from deque 
    // which are less than
    // the current element
    while (dq.Count!=0 && 
           a[dq.Peek()] <= x)
      dq.Dequeue();
 
    // Insert current 
    // index in deque
    dq.Enqueue(i);
 
    // Update current window sum
    s += x;
 
    // Calculate required operation to
    // make current window elements equal
    long cost = (long)a[dq.Peek()] * 
                (answer + 1) - s;
 
    // If cost is less than k
    if (cost <= (long)k)
      answer++;
 
    // Shift window start pointer towards
    // right and update current window sum
    else
    {
      if (dq.Peek() == start)
        dq.Dequeue();
      s -= a[start++];
    }
  }
 
  // Return answer
  return answer;
}
 
// Driver Code
public static void Main(String[] args)
{
  int[] a = {2, 2, 4};
  int k = 10;
 
  // Function call
  Console.WriteLine(maxSubarray(a, k));
}
}
 
// This code is contributed by gauravrajput1

Javascript

<script>
 
// Javascript program for above approach
 
// Function to find the maximum length
// of subarray of equal elements after
// performing at most K increments
function maxSubarray(a, k, n)
{
 
    // Stores the size
    // of required subarray
    var answer = 0;
 
    // Starting point of a window
    var start = 0;
 
    // Stores the sum of window
    var s = 0;
 
    var dq = [];
 
    // Iterate over array
    for(var i = 0; i < n; i++) 
    {
         
        // Current element
        var x = a[i];
 
        // Remove index of minimum elements
        // from deque which are less than
        // the current element
        while (dq.length!=0 &&
               a[dq[0]] <= x)
            dq.shift();
 
        // Insert current index in deque
        dq.push(i);
 
        // Update current window sum
        s += x;
 
        // Calculate required operation to
        // make current window elements equal
        var cost = a[dq[0]] *
                        (answer + 1) - s;
 
        // If cost is less than k
        if (cost <= k)
            answer++;
 
        // Shift window start pointer towards
        // right and update current window sum
        else
        {
            if (dq[0] == start)
                dq.shift();
                 
            s -= a[start++];
        }
    }
     
    // Return answer
    return answer;
}
 
// Driver Code
var a = [2, 2, 4];
var k = 10;
 
// Length of array
var n = a.length;
 
document.write(maxSubarray(a, k, n));
 
 
</script>